Fix qv4jsir_p.h warnings

Apparently CONST is not defined on MSVC 2010, so the unbalanced
push/pop macro usage leads to tons of such warnings:

qv4jsir_p.h(922) : warning C4602: #pragma pop_macro : 'CONST' no
previous #pragma push_macro for this identifier

Change-Id: Ia34ef00e79b4f7a3abf682e1e78dfa3193e30838
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Andreas Holzammer <andreas.holzammer@kdab.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>